U.S. patent application number 13/159736 was filed with the patent office on 2011-12-15 for light-emitting module and illumination device.
This patent application is currently assigned to TOSHIBA LIGHTING & TECHNOLOGY CORPORATION. Invention is credited to Tomohiro Sanpei.
Application Number | 20110305017 13/159736 |
Document ID | / |
Family ID | 44501691 |
Filed Date | 2011-12-15 |
United States Patent
Application |
20110305017 |
Kind Code |
A1 |
Sanpei; Tomohiro |
December 15, 2011 |
LIGHT-EMITTING MODULE AND ILLUMINATION DEVICE
Abstract
According to one embodiment, a light-emitting module comprises a
module substrate, a light-reflecting layer, a plurality of
light-emitting elements, and a sealing material. The module
substrate includes an insulating layer formed of at least one of a
glycidyl ester-type, linear aliphatic epoxide-type, and alicyclic
epoxide-type resin. The light-reflecting layer is superposed on the
insulating layer, and includes a silver light-reflecting surface.
The light-emitting elements are mounted on the module substrate.
The sealing material has light transmittance, and superposed on the
insulating layer to cover the light-reflecting layer and the
light-emitting elements.
Inventors: |
Sanpei; Tomohiro;
(Yokosuka-shi, JP) |
Assignee: |
TOSHIBA LIGHTING & TECHNOLOGY
CORPORATION
Yokosuka-shi
JP
|
Family ID: |
44501691 |
Appl. No.: |
13/159736 |
Filed: |
June 14, 2011 |
Current U.S.
Class: |
362/235 |
Current CPC
Class: |
H01L 33/60 20130101;
H01L 25/0753 20130101; H01L 2224/48091 20130101; F21Y 2115/10
20160801; H01L 2224/73265 20130101; H01L 2224/48091 20130101; H05K
3/284 20130101; H05K 1/056 20130101; H05K 2201/0209 20130101; H01L
2224/48139 20130101; F21K 9/68 20160801; H01L 2924/00014 20130101;
H05K 2201/10106 20130101; H05K 2201/2054 20130101; H01L 2924/00
20130101; H01L 2224/48137 20130101; H01L 2224/48091 20130101 |
Class at
Publication: |
362/235 |
International
Class: |
F21V 7/10 20060101
F21V007/10; F21V 7/22 20060101 F21V007/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 15, 2010 |
JP |
2010-136509 |
Claims
1. A light-emitting module comprising: a module substrate which
includes an insulating layer formed of at least one of a glycidyl
ester-type, linear aliphatic epoxide-type, and alicyclic
epoxide-type resin; a light-reflecting layer which is superposed on
the insulating layer, and includes a sliver light-reflecting
surface that has light reflectance higher than that of the
insulating layer; a plurality of light-emitting elements which are
mounted on the module substrate; and a translucent sealing material
which is superposed on the insulating layer to cover the
light-reflecting layer and the light-emitting elements.
2. The light-emitting module of claim 1, wherein the resin is made
by using acid anhydride as a hardener.
3. The light-emitting module of claim 1, wherein the module
substrate includes a metal base, the base includes a rough surface
on which the insulating layer is superposed.
4. The light-emitting module of claim 3, wherein the
light-reflecting layer includes a metal layer which serves as an
underlayer of the light-reflecting surface, the metal layer
includes a rough mating surface which is superposed on the
insulating layer.
5. An illumination device comprising: a body; a light-emitting
module which is supported by the body; and a lighting device which
is provided in the body and lights the light-emitting module,
wherein the light-emitting module includes: a module substrate
which includes an insulating layer formed of at least one of a
glycidyl ester-type, linear aliphatic epoxide-type, and alicyclic
epoxide-type resin; a light-reflecting layer which is superposed on
the insulating layer, and includes `a sliver light-reflecting
surface that has light reflectance higher than that of the
insulating layer; a plurality of light-emitting elements which are
mounted on the module substrate; and a translucent sealing material
which is superposed on the insulating layer to cover the
light-reflecting layer and the light-emitting elements.
6. The illumination device of claim 5, wherein the module substrate
includes a metal base on which the insulating layer is superposed,
and the body is formed of metal and includes a support surface on
which the base is fixed.
7. The illumination device of claim 6, wherein the module substrate
is thermally connected to the body.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2010-136509, filed
Jun. 15, 2010; the entire contents of which are incorporated herein
by reference.
FIELD
[0002] Embodiments described herein relate generally to a
light-emitting module in which a plurality of light-emitting
elements are mounted on a light-reflecting surface formed of silver
and the like, and an illumination device provided with the
light-emitting module.
BACKGROUND
[0003] Light-emitting modules of the chip-on-a-board (COB) type
include a module substrate, and a plurality of light-emitting
diodes which are mounted on the module substrate. The module
substrate is formed of, for example, glycidyl ether-type epoxy
resin.
[0004] In prior art, to effectively extract light emitted from
light-emitting diodes, it is attempted to superpose a
light-reflecting layer formed of silver on the module substrate.
The light-reflecting layer is used for reflecting light emitted
from the light-emitting diodes toward the module substrate in an
original direction in which the light should be extracted, and the
light-reflecting layer is at least provided in a position which
corresponds to the light-emitting diodes.
[0005] The light-reflecting layer which reflects light emitted from
the light-emitting diodes is required to maintain good light
reflection efficiency for a long period. However, in light-emitting
modules of prior art, the surface of the light-reflecting layer
becomes discolored, blackening with the passage of the lighting
Lime, which causes a decrease in luminous flux.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is an exemplary perspective view of an LED lamp
according to an embodiment;
[0007] FIG. 2 is an exemplary cross-sectional view of the LED lamp
according to the embodiment;
[0008] FIG. 3 is an exemplary plan view of a light-emitting module
according to the embodiment;
[0009] FIG. 4 is an exemplary cross-sectional view of the
light-emitting module according to the embodiment; and
[0010] FIG. 5 is an exemplary characteristic diagram illustrating
relation between the lighting time and the lumen maintenance factor
of the light-emitting module according to the embodiment.
DETAILED DESCRIPTION
[0011] In general according to one embodiment, a light-emitting
module comprises a module substrate, a light-reflecting layer, a
plurality of light-emitting elements, and a sealing material. The
module substrate has an insulating layer formed of at least one of
a glycidyl ester-type, linear aliphatic epoxide-type, and alicyclic
epoxide-type resin. The light-reflecting layer is superposed on the
insulating layer, and has a silver light-reflecting surface which
has light reflectance higher than that of the insulating layer. The
light-emitting elements are mounted on the module substrate. The
sealing material has light transmittance, and is superposed on the
insulating layer to cover the light-reflecting layer and the
light-emitting elements.
[0012] In a light-emitting module of a first aspect, light-emitting
elements indicate light-emitting diodes formed of a bare chip. Each
of light-emitting diodes of this type includes a pair of
electrodes, and bonded onto the light-reflecting surface by using a
die bond material having light transmittance.
[0013] The light-emitting elements are arranged at intervals
between them, and form light-emitting element columns. Each
light-emitting element column is preferably disposed in a straight
line, but may have at least one bent portion which is bent at right
angles between one end and the other end of the light-emitting
element column. Adjacent light-emitting elements are electrically
connected through a plurality of bonding wires. The bonding wires
may be any metal thin wires, preferably copper (Cu) thin wires.
[0014] The light-reflecting surface of the light-reflecting layer
is used for reflecting light emitted from the light-emitting
elements toward the module substrate, and effectively extracting
the light from the light-emitting module. The light-reflecting
surface should have a size on which the light-emitting elements can
be mounted. The light-reflecting layer may be formed of a single
layer or a plurality of layers. It suffices that at least the
surface of the light-reflecting layer is formed of a silver layer.
As the sealing material, it is desirable to use, for example, a
transparent silicone resin. The sealing material is not limited to
silicone resin, but other light-transmitting resin materials can be
used as the sealing material.
[0015] In the light-emitting module of the first aspect, to obtain
white light by using light-emitting elements which emit blue light,
yellow fluorescent material which is excited by blue light and
emits yellow light should be mixed into the sealing material. In
the same manner, to obtain white light by using light-emitting
elements which emit ultraviolet rays, the sealing material should
include a red fluorescent material which is excited by ultraviolet
rays and emits red light, a green fluorescent material which is
excited by ultraviolet rays and emits green light, and a blue
fluorescent material which is excited by ultraviolet rays and emits
blue light.
[0016] In addition, a plurality of light-emitting element
assemblies, each of which is formed of three types of
light-emitting elements that emit red, green, and blue light beams,
may be mounted onto the light-reflecting surface. According to this
structure, light beams emitted from the three light-emitting
elements are mixed together, and white light is emitted from each
light-emitting element assembly. Therefore, it is unnecessary to
mix fluorescent materials into the sealing material.
[0017] In the light-emitting module of the first aspect, the
insulating layer of the module substrate is formed of glycidyl
ester-type, linear aliphatic epoxide-type, or alicyclic
epoxide-type epoxy resin. In epoxy resin of this type, a resin
component which serves as framework of the epoxy resin is
decomposed into gas by light and heat, when the resin receives
light and heat emitted by the light-emitting elements.
[0018] The decomposed gas of the epoxy resin is more resistant to
light and heat than glycidyl ether-type or glycidyl amine-type
epoxy resin, and is difficult to change in quality. Therefore, even
when the decomposed gas adheres to the light-reflecting surface,
there is low possibility that the decomposed gas is carbonized on
the light-reflecting surface. In addition, even when the decomposed
gas is carbonized, the quantity of the carbonized material is
small. Therefore, it is possible to suppress formation of blackish
stains on the light-reflecting surface.
[0019] The insulating layer of the module substrate may be epoxy
resin of any one of glycidyl ester-type, linear aliphatic
epoxide-type and/or alicyclic epoxide-type, or epoxy resin formed
by combining them.
[0020] According to a light-emitting module of a second aspect,
epoxy resin which forms the insulating layer is made by using acid
anhydride as a hardener. Acid anhydride is classified into
aliphatics, alicyclics, aromatics, and halogens. Typical aliphatic
hardeners are dodecenyl succinic anhydride (DDSA), and polyazelaic
polyanhydride (PAPA). Typical alicyclic hardeners are
hexahydrophthalic anhydride (HHPA), methyltetrahydrophthalic
anhydride (MTHPA), and methylnadic anhydride (MNA). Typical
aromatic hardeners are trimet anhydride (TMA), pyromellitic
dianhydride (PDMA), and benzophenonetetracarboxilic dianhydride
(BTDA). Typical halogen hardeners are tetrabromophthalic anhydride
(TBPA), and chlorendic anhydride (HET).
[0021] Epoxy resin can obtain various characteristics by use in
combination with a hardener according to the use. For example, as
epoxy resin for print wiring boards, used are epoxy phenol-type
epoxy resin using phenols as a hardener, epoxy amine-type epoxy
resin using amines as a hardener, and epoxy acid anhydride-type
epoxy resin using acid anhydride as a hardener. In the present
circumstances, epoxy phenol-type epoxy resin is mainly used as
epoxy resin for printed wiring boards.
[0022] The inventor(s) investigated the phenomenon that various
epoxy resins are decomposed by light emitted from blue
light-emitting diodes and the phenomenon that the silver
light-reflecting surface blackens, and found that hardeners of a
certain type are decomposed into gas by light from blue
light-emitting diodes.
[0023] Specifically, in epoxy-phenol-type epoxy resin and epoxy
amine-type epoxy resin, the inventor(s) found that a decomposed
material of the phenol-type resin and amine-type resin used as the
hardener thereof causes blackening of the silver light-reflecting
surface. In addition, the inventor(s) found that epoxy acid
anhydride-type epoxy resin does not cause blackening of the silver
light-reflecting surface even when the acid anhydride being a
hardener is decomposed.
[0024] Therefore, in epoxy acid anhydride-type epoxy resin,
although the resin component of the hardener is decomposed into gas
by light emitted from light-emitting elements, a decomposed
material does not react with the silver light-reflecting surface,
or reacts with a neglectable small quantity. Therefore, it is
possible to prevent the light-reflecting surface from
blackening.
[0025] According to a light-emitting module of a third aspect, the
module substrate includes a metal base. The base includes a rough
surface on which an insulating layer is superposed. The rough
surface of the base has a plurality of minute depressions and
projections.
[0026] According to the above structure, most of the heat produced
by light-emitting elements when the light-emitting elements emit
light is conducted from the insulating layer to the base and
diffused into the base. Therefore, the heat of the light-emitting
elements can be radiated from the base to the outside of the module
substrate, and heat-radiation property of the light-emitting
elements is improved. In addition, since the heat of the
light-emitting elements is radiated from the base, it is possible
to ease heat influence of the light-emitting elements on the
insulating layer. Therefore, the insulating layer is not easily
deteriorated, and the quantity itself of a gaseous decomposed
material produced by the insulating layer is reduced. Thus, it is
possible to suppress change in color of the light-reflecting
surface due to the decomposed material.
[0027] In addition, since the base includes a rough surface, the
insulating layer is engaged with minute depressions and projections
existing on the rough surface of the base. Therefore, it is
possible to secure the bonding strength between the insulating
layer and the base at, for example, 1.0 kgf/mm.sup.2.
[0028] According to a light-emitting module of a fourth aspect, the
light-reflecting surface includes a metal layer which serves as an
underlayer of the light-reflecting surface. The metal layer
includes a rough mating surface which is superposed on the
insulating layer.
[0029] According to the above structure, the insulating layer is
engaged with minute depressions and projections existing on the
rough mating surface of the metal layer. Therefore, it is possible
to secure the bonding strength between the insulating layer and the
metal layer at, for example, 1.0 kgf/mm.sup.2.
[0030] An illumination device according to a fifth aspect
comprises: a light-emitting module described in any one of the
first to fourth aspects; a body which supports the light-emitting
module; and a lighting device which is provided in the body and
lights the light-emitting module.
[0031] In the fifth aspect, the illumination device is an
illumination structure such as an LED lamp which has a shape
similar to an incandescent lamp and a spotlight, and uses the
light-emitting module as a light source.
[0032] According to the illumination device, it is possible to
prevent the light-reflecting surface of the light-emitting module
from blackening, and maintain good light reflection property of the
light-reflecting surface. Therefore, it is possible to efficiently
extract light emitted from the light-emitting elements for a long
period.
[0033] Therefore, it is possible to reduce decrease in luminous
flux of the illumination device to the minimum.
[0034] The following is explanation of the embodiment of the
illumination device, with reference to FIG. 1 to FIG. 5.
[0035] FIG. 1 and FIG. 2 disclose an LED lamp 1 which is an example
of the illumination device. LED lamp 1 comprises a lamp body 2, a
translucent cover 3, an E-shaped base 4, a lighting device 5, and a
chip-on-a-board (COB) light-emitting module 6.
[0036] The lamp body 2 is formed of a metal material such as
aluminum. The lamp body 2 has a tube shape which has a flat support
surface 7 at one end. A ring-shaped support wall 8 is formed as one
unitary piece on an outer edge part of the support surface 7. The
lamp body 2 includes a concave part 9 at the other end which is
opposite to the support surface 7. In addition, a through-hole 11
which extends in an axial direction of the lamp body 2 is formed
inside the lamp body 2. One end of the through-hole 11 is opened to
the support surface 7. The other end of the through-hole 11 is
opened to a bottom of the concave part 9.
[0037] The lamp body 2 includes a plurality of thermally radiative
fins 12. The thermally radiative fins 12 radially project from an
outer peripheral surface of the lamp body 2. In addition, the
thermally radiative fins 12 project toward the outside along the
radial direction of the lamp body 2, as they go from the other end
of the lamp body 2 toward one end.
[0038] The translucent cover 3 is formed in an almost hemispherical
shape of, for example, a milky-white synthetic resin material. The
translucent cover 3 includes an opening edge part 13 which is
opened to the support surface 7 of the lamp body 2. The translucent
cover 3 is connected to the lamp body 2 by fitting the opening edge
part 13 into the support wall 8. The translucent cover 3 covers the
support surface 7 of the lamp body 2.
[0039] As illustrated in FIG. 2, a base support 15 which has
electric non-conductance is attached to the concave part 9 of the
lamp body 2. The base support 15 includes a cylindrical
circumferential wall 15a, and an end wall 15b which closes one end
of the circumferential wall 15a.
[0040] The circumferential wall 15a is fitted into the concave part
9, and covers an internal circumferential surface of the concave
part 9. The circumferential wall 15a includes a projecting part 16
which projects from the concave part 9 to the outside of the lamp
body 2. The end wall 15b covers the bottom of the concave part 9,
and includes a through-hole 17 which agrees with the through-hole
11. In addition, an internal space of the base support 15 connects
to the support surface 7 of the lamp body 2 through the
through-hole 17 and the through-hole 11.
[0041] The base 4 is formed of a metal shell 19, and an insulator
21 which includes an eyelet terminal 20. The shell 19 is attached
to the projecting part 16 of the base support 15 to cover the
projecting part 16 from outside. The insulator 21 abuts on the
opening end part of the projecting part 16, and closes the internal
space of the base support 15.
[0042] The lighting device 5 is contained in the internal space of
the base support 15. The lighting device 5 includes a circuit board
22, and a plurality of circuit components 23 such as a transformer,
a capacitor, and a transistor, which are mounted on the circuit
board 22. The lighting device 5 is electrically connected to the
base 4.
[0043] The light-emitting module 6 is used as a light source of the
LED lamp 1. The light-emitting module 6 is attached to the support
surface 7 of the lamp body 2, and covered with the translucent
cover 3.
[0044] As illustrated in FIG. 3 and FIG. 4, the light-emitting
module 6 includes a module substrate 25. The module substrate 25
has a rectangular shape which has four corners. The module
substrate 25 includes four cutaway parts 25a. The cutaway parts 25a
are located around the respective corners of the module substrate
25.
[0045] As illustrated in FIG. 4, the module substrate 25 is formed
of a metal base 26 and an insulating layer 27. The base 26 is
formed of, for example, aluminum or aluminum alloy. The base 26
includes a first surface 26a and a second surface 26b. The second
surface 26b is located reverse to the first surface 26a, and forms
a front surface of the base 26. The second surface 26b is a rough
surface which includes a plurality of minute depressions and
projections.
[0046] The insulating layer 27 is superposed on the second surface
26b of the base 26, and covers the whole second surface 26b. The
insulating layer 27 is formed of epoxy resin of glycidyl
ester-type, linear aliphatic epoxide-type, or alicyclic
epoxide-type. When epoxy resin of this type receives light and
heat, a resin component which serves as a framework of the epoxy
resin gradually deteriorates and produces a gaseous decomposed
material.
[0047] In the present embodiment, acid anhydride such as
hexahydrophathalic anhydride, methyltetrahydrophthalic acid, and
pyromellitic dianhydride is used as a hardener which is combined
with the epoxy resin. In addition, an inorganic filler such as
aluminum oxide is added to the epoxy resin. The addition ratio of
filler to the epoxy resin is 30 wt %. In addition, in consideration
of reduction of the absolute quantity of the gaseous decomposed
material, the thickness of the insulating layer 27 is preferably
130 .mu.m or less, in particular, 80 .mu.m in view of withstand
voltage.
[0048] In a state where the insulating layer 27 is superposed on
the second surface 26b of the base 26, the insulating layer 27 is
engaged with the minute depressions and projections existing on the
second surface 26b. Therefore, in the present embodiment, the
bonding strength between the insulating layer 27 and the base 26 is
secured at, for example, 1.0 kgf/mm.sup.2.
[0049] The module substrate 25 is fixed in the center of the
support surface 7 of the lamp body 2 by four screws. The screws
pass through the cutaway parts 25a of the module substrate 25 and
driven into the lamp body 2. Thereby, the first surface 26a of the
base 26 is brought into close contact with the support surface 7,
and the module substrate 25 is thermally connected to the lamp body
2.
[0050] As illustrated in FIG. 3 and FIG. 4, a light-reflecting
layer 28, a first power-supply conductor 29, and a second
power-supply conductor 30 are superposed on the insulating layer 27
of the module substrate 25. The light-reflecting layer 28 has a
rectangular shape which has four sides, and is located in the
center of the insulating layer 27. The light-reflecting surface 28
has, for example, a three-layer structure, which is obtained by
combining three metal layers. Specifically, the light-reflecting
layer 28 is formed by stacking a copper layer C, a nickel layer N,
and a silver layer A. The copper layer C is formed by etching a
copper foil superposed on the insulating layer 27. The nickel layer
N is superposed on the copper layer C. The nickel layer N is formed
by subjecting the copper layer C to nonelectrolytic plating. The
silver layer A is superposed on the nickel layer N. The silver
layer A is formed by subjecting the nickel layer N to
nonelectrolytic plating. The silver layer A forms a surface layer
of the light-reflecting layer 28.
[0051] Therefore, the surface of the light-reflecting layer 28 is a
silver light-reflecting surface 32. The light reflectance of the
light-reflecting surface 32 is higher than the light reflectance of
the insulating layer. The total light reflectance of the
light-reflecting surface 32 is, for example, 90.0%.
[0052] The copper layer C which serves as an underlayer of the
light-reflecting surface 32 has a mating surface 33 which contacts
the insulating layer 27. The mating surface 33 is a rough surface
which has a number of minute depressions and projections.
Therefore, in a state where a copper foil which serves as the base
of the copper layer C is superposed on the insulating layer 27, the
insulating layer 27 is engaged with the minute depressions and
projections existing on the mating surface 33. As a result, in the
present embodiment, the bonding strength between the copper layer C
and the insulating layer 27 is secured at, for example, 1.0
kgf/mm.sup.2.
[0053] The structure of the light-reflecting layer 28 is not
limited to the three-layer structure. For example, the
light-reflecting layer 28 may be formed of a single silver layer,
or may have a two-layer structure in which a silver layer is
superposed on a copper layer serving as an underlayer.
[0054] As illustrated in FIG. 3, each of the first and second
power-supply conductors 29 and 30 has an elongated rectangular
shape which extends along a side of the light-reflecting layer 28.
The first and second power-supply conductors 29 and 30 have the
same size. Each of the first and second power-supply conductors 29
and 30 has a three-layer structure which includes a copper layer C,
a nickel layer N, and a silver layer A, in the same manner as the
light-reflecting layer 28. A surface layer of each of the first and
second power-supply conductors 29 and 30 is formed of silver.
[0055] In addition, the first and second power-supply conductors 29
and 30 are arranged in parallel and apart from each other, to hold
the light-reflecting layer 28 therebetween. A slit-shaped space 34a
is provided between the light-reflecting layer 28 and the first
power-supply conductor 29. The space 34a electrically insulates the
light-reflecting layer 28 from the first power-supply conductor 29.
In the same manner, a slit-shaped space 34b is provided between the
light-reflecting layer 28 and the second power-supply conductor 30.
The space 34b electrically insulates the light-reflecting layer 28
from the second power-supply conductor 30. The spaces 34a and 34b
are located on the insulating layer 27. Therefore, part of the
insulating layer 27 is exposed through the spaces 34a and 34b.
[0056] A plurality of light-emitting diode columns 36 are mounted
on the light-reflecting surface 32 of the light-reflecting layer
28. The light-emitting diode columns 36 extend in straight lines in
a direction perpendicular to the first and second power-supply
conductors 29 and 30, and are arranged in parallel at
intervals.
[0057] Each of the light-emitting diode columns 36 includes a
plurality of light-emitting diodes 37 and a plurality of first
bonding wires 38. The light-emitting diodes 37 are an example of
light-emitting elements. Each of the light-emitting diodes 37 is
formed of a bare chip which includes a light-emitting layer 37a
which emits, for example, blue light. Each light-emitting diode 37
has a rectangular shape in a plan view, the longer sides thereof
has a length of, for example, 0.5 mm, and the shorter sides thereof
has a length of 0.25 mm. Each light-emitting diode 37 includes a
pair of electrodes 37b, which have different polarities, on the
light-emitting layer 37a. FIG. 4 illustrates only one of the
electrodes 37b in each light-emitting diode 37.
[0058] Each light-emitting diode 37 is bonded onto the
light-reflecting surface 32 by using a translucent die bond
material. In addition, the light-emitting diodes 37 of each
light-emitting diode column 36 are arranged at intervals in a line
in the direction perpendicular to the first and second power-supply
conductors 29 and 30. As a result, as illustrated in FIG. 3, the
light-emitting diodes 37 are regularly arranged in rows and columns
to spread over a wide range of the light-reflecting surface 32.
[0059] In other words, the light-reflecting surface 32 has a
sufficient size on which all the light-emitting diodes 37 can be
bonded together. Therefore, the light-reflecting surface 32
continues between adjacent light-emitting diodes 37 without a
break. As a result, the insulating layer 27 under the
light-reflecting surface 32 is not exposed from any space between
adjacent light-emitting diodes 37.
[0060] Each first bonding wire 38 electrically connects
light-emitting diodes 37, which are adjacent in a direction where
the light-emitting diode column 36 extends, in series.
Specifically, each first bonding wire 38 extends over adjacent
light-emitting diodes 37 to connect the electrodes 37b having
different polarities of the adjacent light-emitting diodes 37.
[0061] One end of each light-emitting diode column 36 is
electrically connected to the first power-supply conductor 29
through a second bonding wire 40a. In the same manner, the other
end of each light-emitting diode column 36 is electrically
connected to the second power-supply conductor 30 through a third
bonding wire 40b. Therefore, the light-emitting diode columns 36
are electrically connected to the first and second power-supply
conductor 29 and 30 in parallel.
[0062] As illustrated in FIG. 3, a pair of power-supply terminals
42a and 42b are arranged on the insulating layer 27 of the module
substrate 25. The power-supply terminals 42a and 42b are arranged
in a position out of the light-reflecting surface 32. One
power-supply terminal 42a is electrically connected to the first
power-supply conductor 29 through a conductor pattern (not shown).
The other power-supply conductor 42b is electrically connected to
the second power-supply conductor 30 through a conductor pattern
(not shown).
[0063] In addition, a connector 43 is soldered to the power-supply
terminals 42a and 42b. The connector 43 is electrically connected
to the lighting device 5 through a coated electrical wire 44
illustrated in FIG. 2. The coated electrical wire 44 is guided to
the internal space of the base 4, through the through-hole 11 of
the lamp body 2 and the through-hole 17 of the base support 15.
[0064] As illustrated in FIG. 3 and FIG. 4, a frame member 45 is
fixed onto the insulating layer 27. The frame member 45 is formed
of an insulating material such as synthetic resin, and encloses the
light-reflecting layer 28, and the first and second power-supply
conductors 29 and 30 all together. In other words, the
light-emitting diodes 37, and the first to third bonding wires 38,
40a, and 40b are contained in a rectangular area enclosed by the
frame member 45.
[0065] In addition, the frame member 45 is slightly distant from an
outer edge of the light-reflecting layer 28, an outer edge of the
first power-supply conductor 29, and an outer edge of the second
power-supply conductor 30. Therefore, part of the insulating layer
27 is exposed in the area enclosed by the frame member 45.
[0066] A sealing material 46 fills the area enclosed by the frame
member 45. The sealing material 46 is formed of a translucent resin
material such as a transparent silicone resin. The resin material
in a liquid state is injected into the area enclosed by the frame
member 45. The sealing material 46 injected into the area is heated
and dried, and thereby hardened.
[0067] As a result, the sealing material 46 is superposed on the
insulating layer 27 to cover the light-reflecting layer 28, the
first power-supply conductor 29, the second power-supply conductor
30, the light-emitting diodes 37, and the first to third bonding
wires 38, 40a, and 40b. Therefore, the sealing material 46
continuously covers the part of the insulating layer 27 which is
exposed in the area enclosed by the frame member 45.
[0068] In the present embodiment, a fluorescent material is mixed
into the sealing material 46. The fluorescent material is uniformly
dispersed in the sealing member 46. As the fluorescent material,
yellow fluorescent material which is excited by blue light emitted
by the light-emitting diodes 37 and emits yellow light is used.
[0069] The fluorescent material mixed into the sealing material 46
is not limited to yellow fluorescent material. For example, red
fluorescent material which is excited by blue light and emits red
light or green fluorescent material which emits green light may be
added to the sealing member 46, to improve color rendering
properties of the light emitted by the light-emitting diodes
37.
[0070] In the LED lamp 1 having the above structure, a voltage is
applied to the light-emitting module 6 through the lighting device
5. Consequently, the light-emitting diodes 37 on the
light-reflecting layer 28 emit light all together. Blue light
emitted by the light-emitting diodes 37 is made incident on the
sealing member 46. Part of the blue light which is made incident on
the sealing member 46 is absorbed into the yellow fluorescent
material. The rest of the blue light does not collide with the
yellow fluorescent material, but passes through the sealing
material 46.
[0071] The yellow fluorescent material which has absorbed the blue
light is excited and emits yellow light. The yellow light passes
through the sealing material 46. Consequently, the yellow light and
the blue light are mixed together inside the sealing material 46,
and changed to white light. The white light is radiated from the
sealing member 46 toward the translucent cover 3. Therefore, the
sealing material 46 which fills the area enclosed by the frame
member 45 functions as a surface light-emitting part.
[0072] Light which is emitted from the light-emitting diodes 37
toward the module substrate 25 is reflected by the light-reflecting
surface 32 of the light-reflecting layer 28, and surfaces of the
first and second power-supply conductors 29 and 30, and goes toward
the translucent cover 3. Consequently, most of the light emitted
from the light-emitting diodes 37 is transmitted through the
translucent cover 3 and used for illumination.
[0073] Heat of the light-emitting diodes 37, which is produced when
the light-emitting diodes 37 emit light, is conducted to the
light-reflecting layer 28 which is formed by combining three types
of metals. The light-reflecting layer 28 functions as a heat
spreader which spreads heat of the light-emitting diodes 37 over a
wide range. In addition, the heat of the light-emitting diodes 37,
which is spread by the light-reflecting layer 28 is conducted to
the metal base 26 through the insulating layer 27, and conducted to
the support surface 7 of the lamp body 2 through the base 26. The
heat conducted to the lamp body 2 is discharged from the thermally
radiative fins 12 to the outside of the LED lamp 1.
[0074] Consequently, heat of the light-emitting diodes 37 can be
actively released from the module substrate 25 to the lamp body 2.
Therefore, it is possible to enhance the heat radiation property of
the light-emitting diodes 37, and maintain good luminous efficacy
of the light-emitting diodes 37.
[0075] According to the light-emitting module 6 having the above
structure, part of the insulating layer 27 formed of epoxy resin is
exposed in the inside area of the frame member 45 which defines the
light-emitting part of the light-emitting module 6, and covered
with the sealing member 46. Therefore, it is inevitable that part
of light emitted from the light-emitting diodes 37 is made incident
on the insulating layer 27, and heat of the light-emitting diodes
37 is conducted to the insulating layer 27 through the
light-reflecting layer 28.
[0076] When the epoxy resin which forms the insulating layer 27
receives light and heat, the resin component which serves as a
framework of the epoxy resin is gradually deteriorated, and
produces a gaseous decomposed material. Glycidyl ester-type, linear
aliphatic epoxide-type, and alicyclic epoxide-type epoxy resins
used in the present embodiment are not exceptions, and their resin
components which serve as frameworks thereof are decomposed by
light and heat and produce a gaseous decomposed material.
[0077] However, gaseous decomposed materials of glycidyl
ester-type, linear aliphatic epoxide-type, and alicyclic
epoxide-type epoxy resins are more resistant to light and heat than
that of glycidyl ether-type and glycidyl amine-type epoxy resins
which are mainly used in prior art, and are difficult to
deteriorate.
[0078] Therefore, even when the gaseous decomposed material adheres
to the light-reflecting surface 32, there is low possibility that
the decomposed material is carbonized on the light-reflecting
surface 32. In addition, even if the decomposed material is
carbonized, a quantity of the carbonized material is small.
Therefore, blackish stains are not easily formed on the
light-reflecting surface 32, and it is possible to maintain good
light reflectance of the light-reflecting surface 32.
[0079] In particular, in the epoxy resin of the present embodiment,
acid anhydride is used as a hardener. According to investigation by
the inventor(s), it has been verified that decomposed components of
phenol-type resin and amine-type resin which are used as hardeners
in epoxy phenol-type epoxy resin and epoxy amine-type epoxy resin
cause blackening of the silver light-reflecting surface. In
comparison with this, it has been verified that epoxy resin using
acid anhydride as a hardener does not cause blackening of the
silver light-reflecting surface, even when the acid anhydride is
decomposed.
[0080] Therefore, in epoxy resin using an acid anhydride-type
hardener, there is no reaction between a decomposed component of
the hardener and the silver light-reflecting surface 32, or they
react with each other with a neglectable quantity. Therefore, from
the viewpoint of preventing the light-reflecting surface 32 from
blackening, it is desirable to use glycidyl ester-type, linear
aliphatic epoxide-type or alicyclic epoxide-type epoxy resin in
combination with an acid anhydride-type hardener.
[0081] In addition, since the insulating layer 27 is superposed on
the metal base 26, heat of the light-emitting diodes 37 is easily
conducted from the insulating layer 27 to the base 26. This
structure reduces heat influence of the light-emitting diodes 37 on
the insulating layer 27, and thus the insulating layer 27 is not
easily deteriorated. Therefore, the gaseous decomposed material
itself produced by the insulating layer 27 is reduced in quality,
which is convenient for suppressing discoloration of the
light-reflecting surface 32 due to the decomposed material.
[0082] According to the above structure, the LED lamp 1 which
includes the light-emitting module 6 can efficiently extract light
emitted from the light-emitting module 6 via the translucent cover
3, and maintain an expected light output for a long period.
[0083] The inventor(s) performed the following experiment to verify
superiority of the light-emitting module 6 which includes the
insulating layer 27 formed of glycidyl ester-type, linear aliphatic
epoxide-type, or alicyclic epoxide-type epoxy resin.
[0084] In the experiment, a light-emitting module which has the
structure of the present embodiment, and a light-emitting module
which serves as a comparative example and includes an insulating
layer using phenol amine-type resin or amine-type resin as a
hardener were prepared, and the both light-emitting modules were
continuously made emit light (lit) for 1,000 hours.
[0085] FIG. 5 illustrates lumen maintenance factors obtained when
the light-emitting module of the present embodiment and the
light-emitting module of the comparative example were continuously
made emit light for 1,000 hours. In FIG. 5, X indicates transition
of a lumen maintenance factor obtained from the light-emitting
module of the present embodiment. Y indicates transition of a lumen
maintenance factor obtained from the light-emitting module of the
comparative example.
[0086] The term "lumen maintenance factor" indicates a ratio of
luminous flux at initial light emission when the light-emitting
module first emits light to luminous flux at the time when 1,000
hours has passed from the initial light emission. As is clear from
FIG. 5, according to the light-emitting module having the structure
of the present embodiment, the lumen maintenance factor is secured
at 98% or more even when the lighting time reaches 1,000 hours.
[0087] In comparison with this, the lumen maintenance factor of the
light-emitting module of the comparative example decreases to about
94% when 1,000 hours has passed. This fact shows that the
light-emitting module having the structure of the present
embodiment improves the lumen maintenance factor by about 4%.
[0088] In addition, the life of light-emitting modules is generally
set to about 40,000 hours in proper use. Therefore, in view of the
tendency of decrease in lumen maintenance factor at the time when
1,000 hours has passed from the initial light emission, there is
the fear that the lumen maintenance factor of the light-emitting
module of the comparative example at the time when 40,000 hours has
passed from the initial light emission is greatly lower than 80%,
at which ideal brightness is obtained as ordinary illumination.
[0089] In comparison with this, it was found that the luminous
maintenance factor of the light-emitting module having the
structure of the present embodiment still maintained a high value
of 98% or more even at the time when 40,000 hours has passed from
the initial light emission.
[0090] It is considered that this is because blackening of the
light-emitting surface is suppressed in the light-emitting module
of the present embodiment, even when a gaseous decomposed material
is produced from the insulating layer because of light and heat
emitted from the light-emitting diodes. Therefore, it is clear that
a light-emitting surface which is prevented from blackening and has
fewer stains effectively contributes to prevention of decrease in
lumen maintenance factor of the light-emitting module.
[0091] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
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